System and method for selectively energizing catheter electrodes

ABSTRACT

The present invention is directed to a system, a method and a catheter that provide improved ablation capabilities and improved energy efficiency by selectively energizing catheter electrodes on the basis of impedance measurements. In particular, the invention is directed to the selective energization of catheter radial electrodes that together with a tip electrode form a generally continuous tissue contact surface, wherein the selection is made on the basis of impedance measurement as an indication of the amount of tissue contact of each radial electrode.

CROSS-REFERENCE TO RELATED APPLICATION(S)

This application is a continuation of and claims priority to and thebenefit of U.S. patent application Ser. No. 15/811,496 filed Nov. 13,2017, issued as U.S. Pat. No. 10,231,780, which is a continuation of andclaims priority to and the benefit of U.S. patent application Ser. No.15/369,781 filed Dec. 5, 2016, issued as U.S. Pat. No. 9,814,524, whichis a continuation of and claims priority to and the benefit of14/985,239 filed Dec. 30, 2015, issued as U.S. Pat. No. 9,510,893, whichis a continuation of and claims priority to and the benefit of U.S.patent application Ser. No. 14/081,957 filed Nov. 15, 2013, issued asU.S. Pat. No. 9,226,793, which is a continuation of and claims priorityto and the benefit of U.S. patent application Ser. No. 12/985,254, filedJan. 5, 2011, issued as U.S. Pat. No. 8,603,085, which is a continuationof and claims priority to and the benefit of U.S. patent applicationSer. No. 11/322,591, filed Dec. 30, 2005, now U.S. Pat. No. 7,879,029,the entire contents of all of which are incorporated herein byreference.

FIELD OF THE INVENTION

The present invention is directed to a catheter for electric diagnosisand treatment of the heart, and more particularly to a catheter formapping and ablation.

BACKGROUND OF THE INVENTION

Cardiac arrhythmias, the most common of which is ventricular tachycardia(VT), are a leading cause of death. In a majority of patients, VToriginates from a 1 mm to 2 mm lesion located close to the inner surfaceof the heart chamber. One of the treatments for VT comprises mapping theelectrical pathways of the heart to locate the lesion followed byablation of the active site.

U.S. Pat. No. 5,546,951; U.S. patent application Ser. No. 08/793,371;and PCT application WO 96/05768, which are incorporated herein in theirentirety by reference, disclose methods for sensing an electricalproperty of heart tissue such as local activation time as a function ofthe precise location within the heart. The data are acquired byadvancing into the heart one or more catheters that have electrical andlocation sensors in their distal tips. The precise three-dimensionallocation of the catheter tip is ascertained by the location sensorcontained therein. The location sensor operates by generating signalsthat are responsive to its precise location within an externallygenerated non-ionizing field such as an electromagnetic field.Simultaneous with the acquisition of location information, electricalinformation is also acquired by at least one electrode contained at thecatheter distal tip. Accurate sensing of location and electricalinformation by sensors contained in the catheter generally requires ahigh degree of confidence that a catheter electrode is in contact withthe tissue.

Methods of creating a map of the electrical activity of the heart basedon these data are disclosed in U.S. patent application Ser. Nos.09/122,137 and 09/357,559 filed on Jul. 24, 1998 and Jul. 22, 1999,respectively, and in European Patent Application 974,936 which are alsoincorporated herein in their entirety by reference. In clinicalsettings, it is not uncommon to accumulate data at 100 or more siteswithin the heart to generate a detailed, comprehensive map of heartchamber electrical activity. The use of the location sensors ashereinabove described is highly useful in providing a detailed andaccurate map of the heart chamber's activity.

Catheters containing position or location sensors may also be used todetermine the trajectory of points on the cardiac surface. Thesetrajectories may be used to infer mechanical motion characteristics suchas the contractility of the tissue. As disclosed in U.S. Pat. No.5,738,096 which is incorporated herein in its entirety by reference,maps depicting such motion characteristics, which may be superimposedwith maps depicting local electrical information, may be constructedwhen the trajectory information is sampled at a sufficient number ofpoints in the heart. Accurate maps of such motion characteristics againrequire confidence that the data are acquired when the catheter tip isin contact with the cardiac tissue.

The detailed maps generated as hereinabove described may serve as thebasis for deciding on a therapeutic course of action, for example,tissue ablation, to alter the propagation of the heart's electricalactivity and to restore normal heart rhythm. In cardiac ablation,energy, typically in the radiofrequency (RF) range, is supplied atselected points on the intracardiac surface by a catheter having anablation electrode at its distal tip. Ablation is effected by bringingthe distal tip electrode into contact with the locus of aberrantelectrical activity and by initiating the delivery of RF energy throughthe distal tip electrode from an external RF generator in communicationwith the distal tip electrode. Ablation is most effectively performedwhen the distal tip electrode is in contact with the cardiac wall.Absence of contact or poor contact of the tip electrode with the heartwall leads to dissipation of the RF energy in the blood, as well aspossible fouling of the tip electrode with the concomitant possibilityof blood clot formation. Accordingly, it is important that both mappingand ablation be accompanied by methods and systems for detecting andensuring electrode-tissue contact.

A number of references have reported methods to determineelectrode-tissue contact, including U.S. Pat. Nos. 5,935,079; 5,891,095;5,836,990; 5,836,874; 5,673,704; 5,662,108; 5,469,857; 5,447,529;5,341,807; 5,078,714; and Canadian Patent Application 2,285,342. Anumber of these references, e.g., U.S. Pat. Nos. 5,935,079, 5,836,990,5,447,529, and 6,569,160 determine electrode-tissue contact by measuringthe impedance between the tip electrode and a return electrode. Asdisclosed in the '160 patent, the entire disclosure of which is herebyincorporated by reference, it is generally known that impedance throughblood is generally lower that impedance through tissue. Accordingly,tissue contact has been detected by comparing the impedance valuesacross a set of electrodes to pre-measured impedance values when anelectrode is known to be in contact with tissue and when it is known tobe in contact only with blood.

A disadvantage of typical ablation electrodes is that it is sometimesdifficult to accurately predict lesion size because the lesion size canvary depending on the orientation of the ablation electrode. Forexample, typically a 7 French catheter (having an outer diameter of justover 2 mm) is provided with an ablation tip electrode at its distal endhaving a length ranging from about 4 mm to about 8 mm. If the ablationelectrode is provided in perpendicular relation to the tissue, arelatively small surface area of the electrode is in contact with thetissue. In contrast, a relatively larger surface area would be incontact with the tissue if the ablation electrode were in a generallyparallel relationship to the tissue, i.e., if the ablation electrodewere positioned on its side. The size of the lesion is often related tothe amount surface area in contact with the tissue and there can besignificant energy loss through the portion of the electrode not incontact with any tissue, particularly since blood has a higherconductivity than tissue.

Moreover, overheating of the tip electrode can cause complications,including the formation of char and/or thrombus on the electrodesurface. The creation of char and thrombus is unsafe, as the char andthrombus can be dislodged from the electrode during the procedure orduring removal of the catheter after the procedure.

SUMMARY OF THE INVENTION

The present invention is directed to a system, a method and a catheterthat provide improved ablation capabilities and improved energyefficiency by selectively energizing catheter electrodes on the basis ofimpedance measurements. In particular, the invention is directed to theselective energization of catheter radial electrodes that together witha tip electrode form a generally continuous tissue contact surface,wherein the selection is made on the basis of impedance measurement asan indication of the amount of tissue contact of each radial electrode.

The system for selectively energizing electrodes on a catheter includesa catheter having a catheter body, and a tip section carrying a tipelectrode and a plurality of radial electrodes and a return electrode.There are also a signal generator to provide impedance test signals anda multiplexer adapted to operate in a first mode wherein the multiplexercontinuously changes electrical connection between the signal generatorto a specific radial electrode, and a second mode wherein themultiplexer connects the signal electrode to a selected radialelectrode. Further included in the system are an impedance measurementcircuitry adapted to provide impedance measurements of each radialelectrodes as an indication of tissue contact, and a microcontrolleradapted to command the multiplexer to operate in said first mode or saidsecond mode. An ablation energy source is also provided to energize thetip electrode and the selected radial electrode.

The method of the present invention includes providing a catheter havinga catheter body, and a tip section carrying a tip electrode and aplurality of radial electrodes proximal the tip electrode, and providinga return electrode. The method further includes providing a signalgenerator adapted to generate impedance test signals, and changingelectrical connection between the signal generator and a specific radialelectrode. The method further includes obtaining impedance measurementfor each radial electrode when it is receiving impedance test signals asan indication of tissue contact, and identifying the radial electrodewith the highest impedance measurement. The method further includesmaintaining electrical connection between the signal generator and theradial electrode with the highest impedance measurement the exclusion ofremaining radial electrodes, and applying ablation energy to the radialelectrode with the highest impedance to the exclusion of nonselectedradial electrodes.

A catheter of the present invention includes a catheter body having anouter wall, proximal and distal ends, and a single central lumenextending therethrough and a control handle at the proximal end of thecatheter body. Also included are a tip section comprising a segment offlexible tubing having proximal and distal ends and at least one lumentherethrough, the proximal end of the tip section being fixedly attachedto the distal end of the catheter body, and a tip electrode fixedlyattached to the distal end of the tubing of the tip section. Moreover, aplurality of radial electrodes are fixedly attached to the tubingimmediately proximal the tip electrode, wherein each radial electrode isconfigured to form a specific generally continuous tissue contactsurface with the tip electrode.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features and advantages of the present invention will bebetter understood by reference to the following detailed descriptionwhen considered in conjunction with the accompanying drawings wherein:

FIG. 1 is a side elevational view of an embodiment of a catheter inaccordance with the present invention;

FIG. 2 is a side cross sectional view of an embodiment of a catheterbody and an intermediate section taken along a first diameter;

FIG. 2A is a side cross sectional view of the catheter body andintermediate section of FIG. 2 taken along a second diameter generallyperpendicular to the first diameter;

FIG. 3A is a side cross sectional view of an embodiment of theintermediate section and a tip section taken along a first diameter;

FIG. 3B is a side cross sectional view of the intermediate section andthe tip section of FIG. 3A, taken along a second diameter generallyperpendicular to the first diameter;

FIG. 3C is a longitudinal cross sectional view of the intermediatesection of FIG. 3A, taken along line 3C-3C;

FIG. 4A is a side cross sectional view of an embodiment of a tipsection;

FIG. 4B is a longitudinal cross-sectional view of the tip section ofFIG. 4A taken along line 4B-4B;

FIG. 5 is a schematic perspective view of an embodiment of the catheterof the present invention in tissue contact for ablating and creating alesion;

FIG. 6 is a side cross-sectional view of an embodiment of a controlhandle;

FIG. 7 is a schematic diagram of an embodiment of a system forselectively energizing catheter electrodes in accordance with thepresent invention; and

FIG. 8 is a flow chart illustrating schematically a method ofselectively energizing catheter electrodes in accordance with thepresent invention.

DETAILED DESCRIPTION OF THE INVENTION

The present invention provides a system and method and a catheter foruse therewith that ablates with improved energy efficiency. Theinvention is directed to the selective energization of catheter radialelectrodes that together with a tip electrode form a generallycontinuous tissue contact surface, wherein the selection is made on thebasis of impedance measurement as an indication of the amount of tissuecontact of each radial electrode.

With reference to FIG. 1, the catheter 10 comprises an elongatedcatheter body 12 having proximal and distal ends, an intermediatesection 14 at the distal end of the catheter body, a control handle 16at the proximal end of the catheter body, and an irrigated tip section26 at the distal end of the catheter body. The tip section carries a tipelectrode 28 and a plurality of radial electrodes 37 immediatelyproximal the tip electrode. The tip section 26 of the catheter may alsocarry an electromagnetic location sensor 72 to determine the positionand orientation of the catheter within the patient's body.

With reference to FIGS. 2 and 2A, the catheter body 12 comprises anelongated tubular construction having a single, axial or central lumen18. The catheter body 12 is flexible, i.e., bendable, but substantiallynon-compressible along its length. The catheter body 12 can be of anysuitable construction and made of any suitable material. A presentlypreferred construction comprises an outer wall 20 made of polyurethaneor PEBAX. The outer wall 20 comprises an imbedded braided mesh ofstainless steel or the like to increase torsional stiffness of thecatheter body 12 so that, when the control handle 16 is rotated, theintermediate section 14 of the catheter 10 will rotate in acorresponding manner.

The outer diameter of the catheter body 12 is not critical, but ispreferably no more than about 8 french, more preferably 7 french.Likewise the thickness of the outer wall 20 is not critical, but is thinenough so that the central lumen 18 can accommodate at least a pullerwire 50, lead wires 40, 42 and 44, a first irrigating tube segment 88, asensor cable 74. If desired, the inner surface of the outer wall 20 islined with a stiffening tube 22 to provide improved torsional stability.The proximal end of the stiffening tube 22 is affixed to the outer wallby glue joint 15. The distal end of the stiffening tube 22 is affixed tothe outer wall by glue joint 17. A particularly preferred catheter hasan outer wall 20 with an outer diameter of from about 0.090 inch toabout 0.94 inch and an inner diameter of from about 0.061 inch to about0.065 inch.

As shown in FIGS. 3A, 3B and 3C, the intermediate section 14 distal thecatheter body 12 comprises a short section of tubing 19 having multiplelumens. A first lumen 30 carries the electrode lead wires 40, 42 and 44.A second lumen 32 carries the puller wire 50. A third lumen 34 carriesthe sensor cable 74 for the electromagnetic location sensor 72. A fourthlumen 36 allows passage of fluid transported in the first infusion tubesegment 88 and carries a proximal portion of a second infusion tube 89whose distal end is in the tip electrode 28. The tubing 19 is made of asuitable nontoxic material that is preferably more flexible than thecatheter body 12. A presently preferred material for the tubing 19 isbraided polyurethane, i.e., polyurethane with an embedded mesh ofbraided stainless steel or the like. The size of each lumen is notcritical, but is sufficient to house the lead wires, puller wire, thesensor cable or any other components.

The useful length of the catheter, i.e., that portion that can beinserted into the body can vary as desired. Preferably the useful lengthranges from about 110 cm to about 120 cm. The length of the intermediatesection 14 is a relatively small portion of the useful length, andpreferably ranges from about 3.5 cm to about 10 cm, more preferably 6from about 5 cm to about 6.5 cm.

A preferred means for attaching the catheter body 12 to the intermediatesection 14 is illustrated in FIG. 2. The proximal end of theintermediate section 14 comprises an outer circumferential notch 24 thatreceives the inner surface of the outer wall 20 of the catheter body 12.The intermediate section 14 and catheter body 12 are attached by glue orthe like.

If desired, a spacer (not shown) can be located within the catheter bodybetween the distal end of the stiffening tube 22 (if provided) and theproximal end of the intermediate section 14. The spacer provides atransition in flexibility at the junction of the catheter body 12 andintermediate section 14, which allows this junction to bend smoothlywithout folding or kinking. A catheter having such a spacer is describedin U.S. Pat. No. 5,964,757, the disclosure of which is incorporatedherein by reference.

Referring to FIGS. 4A and 4B, at the distal end of the intermediatesection 14 is the tip section 26. Preferably the tip section 26 has adiameter about the same as the outer diameter of the tubing 19. In theillustrated embodiment, the tip section 26 has the tip electrode 28 anda plastic housing or a short section of tubing 35 proximal the tipelectrode 28 for housing the location sensor 72. The proximal end of theplastic housing 35 is received by a circumferential notch 25 (FIGS. 3Aand 3B) formed in the distal end of the tubing 19 and is bonded theretowith polyurethane glue or the like. Preferably the plastic housing isabout 1 cm long.

The tip electrode 28 is generally solid, having a fluid passage 38. Inthe embodiment shown, the fluid passage 38 comprises an axial branch 47and a plurality of transverse branches 48 that extend radially from thedistal end of the axial branch to the outer surface of the tip electrode28. It is understood that the configuration of the fluid passage mayvary as desired.

Formed in the proximal end of the tip electrode 28 is a blind hole 31that generally corresponds in location to the second lumen 32 carryingthe puller wire 50. As described in further detail, the distal end ofthe puller wire and the distal end of the lead wire 40 that connects tothe tip electrode 28 can both be anchored in the blind hole 31. Apreferred tip electrode has an effective length, i.e., from its distalend to the distal end of the tubing 35, of about 3.5 mm, and an actuallength, i.e., from its distal end to its proximal end, of about 4.0 mm.

The tip electrode 28 is attached to the plastic housing 35 by a stem 41formed in the proximal end of the tip electrode 28, which is received bythe distal end of the tubing 35. The stem 41 is affixed with adhesive,glue or the like. The puller wire 50 and the lead wire 40 help keep thetip electrode 28 in place on the tip section 26.

In accordance with the present invention, the tip section 26 carries aplurality of generally equi-sized and equi-angularly spaced, elongatedradial electrodes 37 i. The electrodes 37 i are mounted on the tubing 35of the tip section 26 and in a side-by side configuration to jointlyspan about 360 degrees around the tubing 35. A longitudinal gap betweeneach radial electrodes is provided to electrically isolate each radialelectrode from its adjacent radial electrodes. The gap may be filledwith a non-conducting material 43, for example, polyurethane. As such,the electrodes 37 i cover nearly the entire circumference of the tubing.Moreover, the distal ends of the electrodes 37 i are immediatelyproximal the tip electrode such that the tip electrode 28 and at leastone radial electrode 37 i form a generally continuous elongated contactsurface 53 with tissue 54 when the tip section 26 is oriented at anonperpendicular angle. As shown in FIG. 5, the radial electrode 37 btogether with the tip electrode 28 enable the creation of a largerlesion 59 by providing a larger, generally continuous contact surface 53with the tissue 54. Depending on the tissue surface contour, the size ofthe generally continuous contact surface 53 is typically at a minimumwhere the tip section 26 is generally perpendicular or about 90 degreesto the tissue surface 55 and increases with decreasing angle of the tipsection 28 to the tissue surface 55, with a maximum contact surface areawhere tip section 26 is generally parallel with the tissue surface 55,lying on it, at or about 0 degrees.

As discussed further below, the present invention provides for selectiveenergization of the radial electrode (e.g., electrode 37 b in FIG. 5)that has the most tissue contact for improved energy efficiency duringablation. That is, by withholding the ablation energy from those radialelectrodes with less or no tissue contact (e.g., electrodes 37 a, 37 cand 37 d in FIG. 5), the energy is applied with discretion to minimizeenergy loss to the surrounding blood. In accordance with a feature ofthe invention, by providing n number of radial electrodes 37 a-37 n,each radial electrode possesses a (1/n) fraction of the circumferentialtissue contact surface of the catheter tip section. And, by supplyingthe ablation energy through only one radial electrode (namely, the onehaving the greatest tissue contact), the 1/n surface area of that radialelectrode, by definition, increases the current density, whereupon ahigher current density permits lower power usage and greater efficiencyby the catheter 10.

Because of the location of the tip electrode, it generally makes goodtissue contact, particularly, when it is depressed into the tissue asshown in FIG. 5. Accordingly, in the disclosed embodiment, the tipelectrode 28 consistently receives the ablation energy whenever theablation energy is applied by the operator and is not subject to thisdiscretionary process.

Moreover, by selectively energizing the radial electrodes, the tipsection 26 is rendered less prone to overheating and therefore thetissue is less susceptible to the risks associated with overheating,such as char and thrombus.

It is understood by one of ordinary skill in the art that the number ofradial electrodes may be varied and can range between at least two toabout eight, provided the electrodes jointly span about 360 degreesaround the tubing 35 to cover its circumference. In the illustratedembodiment, there are four “quadrant” electrode 37 a-37 d, eachgenerally rectangular and spanning about 90 degrees around the tubing35. The length of each radial electrode may range between about 4.0 mmand 10 mm, and preferably is about 8.0 mm. It is understood by one ofordinary skill in the art that the width of each radial electrodedepends on the size of the catheter tip section and the number of radialelectrodes.

There may also be ring electrodes 56 carried on the distal section ofthe tubing 19 of the intermediate section 14. In the illustratedembodiment, there are three ring electrodes proximal of the radialelectrodes 37. The ring electrodes 56 allow an operator to collectelectrophysiological data from the tip section 36 of the catheter 10.Accordingly, the presence and number of ring electrodes 56 can vary asdesired.

The tip electrode 28, the radial electrodes 37 and the ring electrodes56 can be made of any suitable material, for example, from machinedplatinum-iridium bar (90% platinum/10% iridium).

Each of the tip electrode 28, the radial electrodes 37, and the ringelectrodes 56 is connected to a separate lead wire. The lead wires 40,42 and 44 extend through the first lumen 30 of intermediate section 14,the central lumen 18 of the catheter body 12, and the control handle 16,and terminate at their proximal end in an input jack (not shown) thatmay be plugged into an appropriate monitor (not shown). The portion ofthe lead wires 40, 42, 44 extending through the central lumen 18 of thecatheter body 12, control handle 16 and the intermediate section 14 areenclosed within a protective, nonconducting sheath 39, which can be madeof any suitable material, preferably polyimide. The sheath 39 isanchored at its distal end to the distal end of the intermediate section14 by gluing it in the first lumen 30 with polyurethane glue or thelike. In the illustrated embodiment, there are two sheaths 39A and 39B.The sheath 39A is dedicated to the lead wire 40 for the tip electrode 28and the lead wires 44 for the ring electrodes 56. The sheath 49B isdedicated to the lead wires 42 for the radial electrodes 37. The distalend of sheath 39B is proximal of the most proximal ring electrode 56.The distal end of the sheath 39A is proximal of the radial electrodes37.

The lead wires 44 and 42 are attached to the radial and ring electrodes37 and 56 by any conventional technique. Connection of a lead wire toone of these electrodes is preferably accomplished by first making asmall hole through the tubing 19 or 35. Such a hole can be created, forexample, by inserting a needle through the tubing and heating the needlesufficiently to form a permanent hole. A lead wire is then drawn throughthe hole by using a microhook or the like. The ends of the lead wire arethen stripped of any coating and soldered or welded to the underside ofthe electrode. The electrodes may then be positioned over the hole (orslid into position over the hole in the case of the ring electrodes) andare fixed in place with polyurethane glue or the like.

The tip section 26 carries the electromagnetic location sensor 72 whichis bonded in the lumen of the tubing 35. The electromagnetic sensorcable 74 extend from the proximal end of the location sensor and throughthe third lumen 34 of the tip section 14, through the central lumen 18of the catheter body 12, and into the control handle 16. As shown inFIG. 1, the electromagnetic sensor cable 74 then extends out theproximal end of the control handle 16 within an umbilical cord 98 to asensor control module 75 that houses a circuit board (not shown).Alternatively, the circuit board can be housed within the control handle16, for example, as described in U.S. Pat. No. 5,964,757, the entiredisclosure of which is incorporated herein by reference. Theelectromagnetic sensor cable 74 comprises multiple wires encased withina plastic covered sheath. In the sensor control module 75, the wires ofthe electromagnetic sensor cable 74 are connected to the circuit board.The circuit board amplifies the signal received from the electromagneticsensor 72 and transmits it to a computer in a form understandable by thecomputer by means of the sensor connector 77 at the proximal end of thesensor control module 75, as shown in FIG. 1. Also, because the catheteris designed for single use only, the circuit board may contain an EPROMchip which shuts down the circuit board approximately 24 hours after thecatheter has been used. This prevents the catheter, or at least theelectromagnetic sensor, from being used twice. Suitable electromagneticsensors for use with the present invention are described, for example,in U.S. Pat. Nos. 5,558,091, 5,443,489, 5,480,422, 5,546,951, 5,568,809,and 5,391,199 and International Publication No. WO 95/02995, thedisclosures of which are incorporated herein by reference. A preferredelectromagnetic mapping sensor 72 has a length of from about 6 mm toabout 7 mm and a diameter of about 1.3 mm.

Referring back to FIG. 2, the puller wire 50 extends through thecatheter body 12, is anchored at its proximal end to the control handle16 (FIG. 6), and is anchored at its distal end to the tip electrode 28(FIG. 4A). The puller wire is made of any suitable metal, such asstainless steel or Nitinol, and preferably has a coating of Teflon® orthe like. The coating imparts lubricity to the puller wire. The pullerwire preferably has a diameter ranging from about 0.006 to about 0.010inches.

A compression coil 52 is situated within the catheter body 12 insurrounding relation to the puller wire 50. The compression coil 52extends from the proximal end of the catheter body 12 to the proximalend of the intermediate section 14. The compression coil 52 is made ofany suitable metal, preferably stainless steel. The compression coil 52is tightly wound on itself to provide flexibility, i.e., bending, but toresist compression. The inner diameter of the compression coil ispreferably slightly larger than the diameter of the puller wire 50. TheTeflon® coating on the puller wire 50 allows it to slide freely withinthe compression coil 52. If desired, particularly if the lead wires 40,42, 44 are not enclosed by a protective sheaths 39, the outer surface ofthe compression coil can be covered by a flexible, non-conductivesheath, e.g., made of polyimide tubing, to prevent contact between thecompression coil 52 and any other wires within the catheter body 12.

The compression coil 52 is anchored at its proximal end to the proximalend of the stiffening tube 22 in the catheter body 12 by glue joint 51and at its distal end to the intermediate section 14 by glue joint 57.Both glue joints 51 and 57 preferably comprise polyurethane glue or thelike. The glue may be applied by means of a syringe or the like througha hole made between the outer surface of the catheter body 12 and thecentral lumen 18. Such a hole may be formed, for example, by a needle orthe like that punctures the outer wall 20 of the catheter body 12 andthe stiffening tube 22 which is heated sufficiently to form a permanenthole. The glue is then introduced through the hole to the outer surfaceof the compression coil 52 and wicks around the outer circumference toform a glue joint about the entire circumference of the compression coil52.

As shown in FIG. 4A, the puller wire 50 is anchored at its distal end tothe tip electrode 28 within the blind hole 31. A preferred method foranchoring the puller wire 50 within the tip electrode 28 is by crimpingmetal tubing 46 to the distal end of the puller wire 50 and solderingthe metal tubing 46 inside the blind hole 31. Anchoring the puller wire50 within the tip electrode 28 provides additional support, reducing thelikelihood that the tip electrode 28 will fall off the tip section 26.Alternatively, the puller wire 50 can be attached to the tubing 35 ofthe tip section 26, or the distal section of the tubing 19 of theintermediate section 14. Within the second lumen 32 of the intermediatesection 14, the puller wire 50 extends through a plastic, preferablyTeflon®, sheath 58, which prevents the puller wire 50 from cutting intothe wall of the tubing 19 when the intermediate section 14 is deflected.

Longitudinal movement of the puller wire 50 relative to the catheterbody 12, which results in deflection of the intermediate section 14, isaccomplished by suitable manipulation of the control handle 16. As shownin FIG. 6, the distal end of the control handle 16 comprises a piston 60with a thumb control 62 for manipulating the puller wire 50. Theproximal end of the catheter body 12 is connected to the piston 60 bymeans of a shrink sleeve 64.

The puller wire 50, lead wires 40, 42, 44, the sensor cable 74 extendthrough the piston 60. The puller wire 50 is anchored to an anchor pin66, located proximal to the piston 60. Within the piston 60, the sensorcable 74 extends into another protective sheath 91, preferably made ofpolyurethane. The protective sheathes 39A, 39B and 91 are anchored tothe piston 60, preferably by polyurethane glue or the like at a gluejoint 63, allowing the lead wires 40, 42, 44 and the sensor cable 74longitudinal movement within the control handle 16 so that they do notbreak when the piston 60 is adjusted to manipulate the puller wire 50.Within the piston 60, the puller wire 50 extends through a transfer tube27, preferably a polyimide tube, to allow longitudinal movement of thepuller wire near the glue joint 63.

The mechanics and operation of the control handle are described in U.S.Pat. No. 6,602,242, the entire disclosure of which is incorporatedherein by reference. It is understood by one of ordinary skill in theart that other control handles for manipulating the puller wire orpuller wires (for bi-directional deflection) may be used with thepresent catheters.

FIG. 7 illustrates a system 100 for performing ablation using thecatheter 10 in selectively energizing the radial electrode having thegreatest tissue contact as identified by the system on the basis ofimpedance measurements. Each of the radial electrodes 37 i is connectedby a separate lead wire 42 i to the catheter handle 16 from whichelectrical connections are made to the system 100. A signal generator(SG) 102 sends a high frequency test signal, e.g., an alternatingcurrent (AC) signal at about 2 μamps, in the frequency range of about 10kHz to about 100 kHz, preferably about 50 kHz, to a multiplexer 104 viaa high output impedance buffer (IB) 106. The multiplexer 104 hasmultiple channels 108 i, each of which is in communication with aspecific radial electrode 37 i to receive the same current.

A return electrode 110 is also driven by the signal generator 102. Thesignal to the return electrode 110 is first inverted in phase byinverter 112 and conditioned by high output impedance buffer (IB) 114.

In accordance with a feature of the invention, the system 100 providesan impedance measurement circuitry (IMC) 115 to measure the impedance ofeach radial electrode as an indicator of the extent of tissue contact ofeach radial electrode. By energizing only the radial electrode with thegreatest impedance measurement, that selected radial electrode and thetip electrode form a greater tissue contact surface than the tipelectrode would by itself and the ablation energy is not wasted on otherradial electrodes that have no or lesser tissue contact. The impedancemeasurement circuitry 115 includes a differential amplifier (DA) 116, anamplifier (AMP) 118 and a synchronous detector (SD) 120. Thedifferential amplifier 116 measures a difference signal, specificallythe voltage across a selected radial electrode 37 i and the returnelectrode 110. The difference signal is further amplified by theamplifier 118 whose output is send to the synchronous detector 120 whichtransforms the AC signal into a direct current (DC) signal and alsodecreases the sensitivity of the system 100 to external noise. Thesignal from the synchronous detector 120 is then used by amicrocontroller 122 to control the multiplexer 104. To that end, themicrocontroller continuously stores in a memory 124 a plurality ofdifferent impedance signals from the synchronous detector 120 thatequals the plurality of channels 108 i in the multiplexer 104 (which isat least the plurality of radial electrodes 37 i on the catheter 10),along with identification information on the channels 108 i associatedwith each impedance value stored. As such, the microcontroller 122 is atany time capable of identifying the channel 108 i (and hence the radialelectrode 37 i) exhibiting the highest impedance value, which should bethe radial electrode 37 i with the greatest tissue contact.

With reference to the flow chart of FIG. 8, the system 100 in operationas implemented by the microcontroller 122 is described as follows. Underfluoroscopic guidance, or other suitable guidance means, the catheter isintroduced into the patient's body. The catheter is advanced into thepatient's heart through appropriate vascular access and positionedinside the heart chamber. The system 100 and microcontroller 122 arepowered up (Block 130). The microcontroller 122 is activates the signalgenerator and commands the multiplexer to operate in the “switch” mode(Block 132), whereby the multiplexer constantly switches between thechannels 108 i and allows passage of the impedance test signal from thesignal generator 102 to only one radial electrode 37 i at any given time(Block 134). The impedance measurement circuitry 115 measures theimpedance of each radial electrode 37 i as the multiplexer 108 switchesbetween the different channels 108 i (Block 136) and the impedancemeasurements are stored in the memory which is constantly being updatedwith new impedance measurements of each radial electrode.

When the operator of the catheter is ready to ablate, he triggers aninput, e.g., a push-to-activate contact 129 (FIG. 7) or the like (Query138), which signals the microcontroller 122 to access the memory 124 andidentify the channel 108 with the greatest impedance value (Block 140).If there are more than one radial electrode with the same greatestimpedance measurement (Block 141), the microcontroller 122 selects themost recent radial electrode with the greatest impedance measurement(Block 142). In any event, the microcontroller 122 then commands themultiplexer 104 to switch to a “lock” (or “stationary”) mode and theconnection of the multiplexer remains on the identified channel (Block143) for the duration of the ablation session.

The microcontroller 122 then enables the ablation power source (PS) 126and the switch 128 (Block 144) which energizes the tip electrode 28 andallows the ablation current to pass to the selected radial electrodewhose lead is receiving the current from the multiplexer 104 (Block146). The combined contact surface of the tip electrode 28 and theselected radial electrode 37 i creates a larger lesion with improvedenergy efficiency because the ablation current is directed to the tipelectrode 28 and only the radial electrode 37 i with the most tissuecontact.

When the operator completes the ablation session, he releases the buttonor switch and the microcontroller 122 deactivates the ablation powersource 126 and the switch 128 (Block 150) and returns the multiplexer104 to operation in the “switch” mode (Block 132). Thus, the multiplexer104 returns to constantly switching between its channel 108 i to allowthe test signal from the signal generator 102 to pass through thedifferent channels onto each radial electrode 37 i. The microcontroller122 returns to receiving impedance signals of each radial electrode 37 ifrom the impedance measurement circuitry 115 and constantly storing andrefreshing the impedance values in the memory 124, along with theidentification information of the channel associated with each storedimpedance values.

The preceding description has been presented with reference to presentlypreferred embodiments of the invention. Workers skilled in the art andtechnology to which this invention pertains will appreciate thatalterations and changes to the described structure may be practicedwithout meaningfully departing from the principal, spirit and scope ofthis invention. Accordingly, the foregoing description should not beread as pertaining only to the precise structures described andillustrated in the accompanying drawings, but rather should be readconsistent with and as support for the following claims which are tohave their fullest and fairest scope.

What is claimed is:
 1. A catheter comprising: an elongated catheterbody; and a tip section having a tip electrode and two or more secondaryelectrodes, the two or more secondary electrodes being configured forselective energization.
 2. The catheter according to claim 1, whereinthe secondary electrodes span side-by-side radially around the tipsection, each separated from each other secondary electrode by a gap. 3.The catheter according to claim 2, wherein the gap includes anon-conducting material.
 4. The catheter according to claim 1, whereinthe two or more secondary electrodes comprises four secondaryelectrodes.
 5. The catheter according to claim 1, further comprising adifferent lead wire for each of the two or more secondary electrodes. 6.The catheter according to claim 1, wherein each of the two or moresecondary electrodes have an elongated form extending longitudinallyalong the tip section.
 7. A system for ablating tissue, comprising: acatheter having a catheter body, and a tip section carrying a tipelectrode and two or more secondary electrodes; a signal generatorconfigured to generate impedance test signals; an impedance measurementcircuity configured to generate impedance measurements of each of thetwo or more secondary electrodes; a multiplexer configured to connectthe signal generator to a selected one of the two or more secondaryelectrodes in response to the impedance measurements; an ablation energysource configured to energize the tip electrode and the selected one ofthe two or more secondary electrodes.
 8. The system according to claim7, wherein each of the two or more secondary electrodes is configured toform a different tissue contact surface with the tip electrode.
 9. Thesystem according to claim 7, wherein the tip electrode is irrigated. 10.The system according to claim 7, wherein the ablation energy source isconfigured to deliver ablation energy to the selected one of the two ormore secondary electrodes to the exclusion of remaining ones of the twoor more secondary electrodes.
 11. The system according to claim 7,further comprising a return electrode.
 12. The system according to claim7, further comprising a memory configured to store the impedancemeasurements.
 13. The system according to claim 12, wherein the memoryis continuously refreshed with new impedance measurements.
 14. Thesystem according to claim 7, wherein the two or more secondaryelectrodes comprises four secondary electrodes.
 15. A method of ablatingtissue, comprising: introducing to the tissue a catheter having acatheter body, and a tip section carrying a tip electrode and two ormore secondary electrodes; obtaining impedance measurements for each ofthe two or more secondary electrodes; identifying which one of the twoor more secondary electrodes has the highest impedance measurement;applying ablation energy to the one of the two or more secondaryelectrodes with the highest impedance measurement to the exclusion ofremaining ones of the two or more secondary electrodes to thereby ablatethe tissue.
 16. The method according to claim 15, wherein each of thetwo or more secondary electrodes is configured to form a differenttissue contact surface with the tip electrode.
 17. The method accordingto claim 15, wherein the tip electrode is irrigated, and the methodfurther comprises irrigating the tip electrode.
 18. The method accordingto claim 15, further comprising storing the impedance measurements in amemory.
 19. The method according to claim 18, further comprisingcontinuously refreshing the memory with new impedance measurements. 20.The method according to claim 1, wherein the two or more secondaryelectrodes comprises four secondary electrodes.